Sexual Reproduction The process of sexual reproduction involves

Sexual Reproduction • The process of sexual reproduction involves two parents. • Both parents normally contribute one gamete or sex cell to the process. • This process assures that the genetic information given to the offspring will be obtained equally from each parent. • The female gamete is called the egg or the ovum and the male gamete is called a sperm. • These gametes are formed in specialized reproductive structures called gonads. • The sperm is much smaller than the egg, but is capable of moving on its own power using a whip-like tail called a flagellum.

• Meiosis The process of meiosis produces gametes or sex cells. • Mitosis produces other cell types. • The process of meiosis halves the chromosome number from the original parent cell in the four cells it forms. • It does this by having two cell divisions forming four cells, where mitosis has only one cell division forming two cells. • Both processes start out with one doubling or replication of the chromosome material.

Tetrad

• Another important way that meiosis differs from mitosis is the exchange of chromosome pieces which occurs in the first division of this process. This exchange of chromosome pieces is called crossing over. • Crossing over assures that the cells produced as a result of meiosis will be different from and exhibit variations from the parent cell that produced them. This process is chiefly responsible for the variations seen in members of the same species of sexually reproducing organisms. These variations are the driving force for the process of natural selection. • The process of crossing over and how it produces variation when these chromosomes are recombined in the process of fertilization is illustrated in the graphic below.

Another important way that meiosis differs from mitosis is the exchange of chromosome pieces which occurs in the first division of this process. This exchange of chromosome pieces is called crossing over. Crossing over assures that the cells produced as a result of meiosis will be different from and exhibit variations from the parent cell that produced them. This process is chiefly responsible for the variations seen in members of the same species of sexually reproducing organisms. These variations are the driving force for the process of natural selection. The process of crossing over produces variation when these chromosomes are recombined.

Male reproductive System The structure and function of the human male reproductive system, is very similar to that of many other mammals. The male system is designed to make sperm or male gamete, make sex hormones, and is adapted to provide for the delivery of these gametes to the female to allow for fertilization.

• Male Reproductive System Structures • 1. testes -- produces sperm and the hormone testosterone • 2. scrotum -- pouch enclosing the testes keeping the sperm at an optimum temperature for development • 3. vas deferens -- tube carrying sperm away from the testes • 4. prostate gland -- the largest of several glands which add lubricating and other fluids to the sperm • -- this combination of sperm and fluids is called semen • 5. urethra -- tube through the penis carrying sperm to the outside of the body • 6. penis -- adaptation for internal fertilization of the female

• Male Reproductive System Structures • 1. testes -- produces sperm and the hormone testosterone • 2. scrotum -- pouch enclosing the testes keeping the sperm at an optimum temperature for development • Epididymis: A coiled tube • 3. vas deferens -- tube carrying sperm away from the testes • 4. prostate gland -- the largest of several glands which add lubricating and other fluids to the sperm • -- this combination of sperm and fluids is called semen • 5. urethra -- tube through the penis carrying sperm to the outside of the body • 6. penis -- adaptation for internal fertilization of the female

Male Reproductive System • •

Male Reproductive system

Female Reproductive system • Ovaries: Make eggs, female sex hormones: estrogen and progesterone • Oviduct/Fallopian tubes: passage for egg to the uterus • Uterus/Womb: where embryo develops • Cervix: opening of uterus into the muscular tube called vagina • Vagina: Birth canal; entry passage for the penis to deposit semen

• Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg) that participates in reproduction

• Female Reproductive System Structures • 1. ovary -- (females have two of these) -- produce female gametes or eggs and the hormone estrogen • 2. oviduct (fallopian tube) -- carries the egg away from the ovary • -- internal fertilization normally occurs here • 3. uterus -- implantation and development of the embryo and fetus before birth occurs here • 4. vagina or birth canal -- entry point for sperm from the male and exit tube for the baby when it is born

FETUS

Human Fetus Exchanges Gases with Mother’s Blood through the Placenta

Placenta

Menstrual cycle • Is a series of events (last for 28 days) that prepares the uterus for pregnancy • Starts with thickening/vascularization of the lining of the uterine wall, and if fertilization (union of egg and sperm) does not happen, ends with the breakdown of the uterine lining (causing the periods/menstruation)

When does the cycle start? • At puberty; when an individual becomes capable of reproduction • Ends/ceases at menopause • Interrupted during pregnancy/or some illnesses

Who are the main players that regulate this cycle? • Hormones • FSH (follicle stimulating hormones) and LH (luteinizing hormone); made by PITUITARY gland • Estrogen and progesterone made by the ovaries

• First, hypothalamus signals Pituitary to make FSH • FSH signals ovaries to make Estrogen…(made by follicle) • High Estrogen levels signal Pituitary to stop making FSH! • Now, pituitary makes Luteinizing Hormone which signals corpus luteum to make progesterone. .

4 stages of menstrual cycle • Follicle stage (1 -14 days) • Ovulation (Day 15) • Luteal stage (10 -12 days) • Menstruation (last 4 -5 days)

Four Stages of menstrual cycle 1 Follicle stage (1 -14 days): Egg in an ovary matures inside a sac called follicle; and follicle secretes estrogen which stimulates the follicle maturation and the thickening of uterine lining

• Ovulation: mature ovarian follicle ruptures and discharges an ovum

Stage 3: Luteal stage(10 -12 days) • Left over follicle (minus egg) becomes corpus luteum • Which now makes progesterone that finishes up the thickening of uterus

Follicle stage • Egg matures…follicle secretes estrogen… How? . . the pituitary gland releases follicle stimulating hormone…FSH, that stimulates follicle to make estrogen • estrogen makes Uterine wall thick by vascularization • Lasts 14 days… Ovulation happens • Now estrogen inhibits the FSH made by pituitary gland…pituitary now starts to make Luteinizing Hormone…LH • Luteal phase • LH stimulates the formation of Corpus luteum • CL makes progesterone which increases the vascularization of the uterine lining…endometrium

4 Stages of the Menstrual cycle • Follicle stage • Ovulation • Corpus Luteum stage • Menstruation 1. Estrogen 2. Progesterone

Stage 4: Menstruation • If fertilization doesn’t happen, the uterus lining breaks down in the next 4 -5 days • That is menstruation • If fertilization happens…

How does the egg develop? (First, it matures and then is released…)

• Ovulation is the process in the menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete, or casually, an egg) that participates in reproduction

What is Fertilization?

Fertilization… • The union of male and female gametes to form a zygote

• The first few divisions of the zygote are called cleavage. • Cleavage is mitotic divisions • Different stages of development of zygote after cleavage: • 1) Hollow ball of cells…blastula • 2) Invagination of blastula makes gastrula…process is called gastrulation

Why doesn’t cleavage result in an increase in the size of the zygote?

What is implantation?

How does embryo (gastrula) develop into a fetus? • By the process of differentiation.

Human Fetus Exchanges Gases with Mother’s Blood through the Placenta

Where does fertilization occur in humans? • Inside the body • Where does the development of baby happen? • Inside the female body • Fertilization and development, both are INTERNAL • It happens in most mammals

Organisms with EXTERNAL fertilization and development? • Organisms which spend their lives or a large proportion of their lives in the water tend to lay their eggs in great numbers (thousands) in the water and wait for the male of the species to release sperm near them to fertilize them. The fertilization which occurs outside the body of the organism is called external fertilization. These young organisms then develop outside the mother in the water once this has occurred, which is called external development. A disadvantage of this process is that the eggs have lesser probability of getting fertilized (hence large numbers) and developing young have little or no parental protection. Many fish and amphibians like frogs undergo fertilization and development in this manner.

Reptiles and birds use the process of internal fertilization to fertilize their eggs. In this situation, the male of the species inserts his sperm inside the female, who then lays her fertilized eggs outside her body. The process of development is external. Reptiles and especially birds tend to lay fewer eggs and provide much more parental protection for their developing young.

Female Reproductive system • Ovaries: Make eggs, female sex hormones: estrogen and progesterone • Oviduct/Fallopian tubes: passage for egg to the uterus • Uterus/Womb: where embryo develops • Cervix: opening of uterus into the muscular tube called vagina • Vagina: Birth canal; entry passage for the penis to deposit semen

• Female Reproductive System Structures • 1. ovary -- (females have two of these) -- produce female gametes or eggs and the hormone estrogen • 2. oviduct (fallopian tube) -- carries the egg away from the ovary • 3. uterus -- implantation and development of the embryo and fetus occurs here • 4. vagina or birth canal -- entry point for sperm from the male and exit tube for the baby when it is born

Why doesn’t cleavage result in an increase in the size of the zygote?

What is implantation? • Is the process by which embryo attaches to the wall of the uterus. • What is the next stage called?

FETUS

Human Fetus Exchanges Gases with Mother’s Blood through the Placenta

How does fetus get food and oxygen? • Through Placenta • How does fetus get rid of waste (carbon dioxide)? • Placenta

Placenta

4 Stages of the Menstrual cycle • Follicle stage • Ovulation • Corpus Luteum stage • Menstruation 1. Estrogen 2. Progesterone

Who tells the egg (follicle) to start maturing? • Hormones control the reproductive cycle. • • Who is the master gland? Pituitary gland Who tells pituitary to start making hormone? HYPOTHALAMUS

• First, hypothalamus signals Pituitary to make FSH • FSH signals ovaries to make Estrogen…(made by follicle) • High Estrogen levels signal Pituitary to stop making FSH! • Now, pituitary makes Luteinizing Hormone which signals corpus luteum to make progesterone. .

Follicle stage • Egg matures…follicle secretes estrogen… How? . . the pituitary gland releases follicle stimulating hormone…FSH, that stimulates follicle to make estrogen • estrogen makes Uterine wall thick by vascularization • Lasts 14 days… Ovulation happens • Now estrogen inhibits the FSH made by pituitary gland…pituitary now starts to make Luteinizing Hormone…LH • Luteal phase • LH stimulates the formation of Corpus luteum which makes progesterone that increases the vascularization of the uterine lining…endometrium

Organisms with EXTERNAL fertilization and development? • Organisms which spend their lives or a large proportion of their lives in the water tend to lay their eggs in great numbers (thousands) in the water and wait for the male of the species to release sperm near them to fertilize them. The fertilization which occurs outside the body of the organism is called external fertilization. These young organisms then develop outside the mother in the water once this has occurred, which is called external development. A disadvantage of this process is that the eggs have lesser probability of getting fertilized (hence large numbers) and developing young have little or no parental protection. Many fish and amphibians like frogs undergo fertilization and development in this manner.